A fabric-resin system such as fibreglass is popularly used as the primary component in the manufacture of boats, because of both its versatility and its weather-resistant qualities. For decades many of the structural components of pleasure boats have been manufactured from fibreglass or another fabric-resin system, for example more recently, carbon-graphite. In such systems a fabric formed from fibres of the selected composition is laid over a mold, and impregnated with a curable resin which, when cured, imparts rigidity to the fabric and adheres it to adjacent fabric layers. Through the overlapping of adjacent fabric pieces and the building of successive layers, a strong and waterproof structural coating is produced that is also resistant to weather and general wear and tear.
One of the most common boat components manufactured from a fabric-resin system is the mast. A simple mast, usually found on a small pleasure sailboat, is cylindrical. The mast in a large (e.g. 100 foot) pleasure sailboat is rarely cylindrical, as it has been found that an oval cross-section is more aerodynamic. The aerodynamic characteristics of the mast are thus more important in an oval mast, which can be fixed, the base of the mast being bolted directly to the boat deck so that the mast experiences variable drag depending upon the angle of the boat to the wind; or rotating (more common on a multi-hull boat), whereby the mast is mounted on a rotary joint and is capable of turning to minimize drag as the orientation of the boat changes relative to the wind. In either case the mast must be self-standing, and must not only carry the full weight of the mainsail, but must also resist the moment of force imparted by the wind when the mainsail is fully unfurled, which can be considerable.
In a large pleasure sailboat the mast can approach the length of the boat, and is anchored only at its base. As such, the mast must be able to bear significant forces over its entire length, and preferably should be able to flex to accommodate a sudden change in the direction of the force. Fabric-resin systems are ideal for such a structural member, as they tend to be light but very strong and weather-resistant, and suitably flexible. Carbon-graphite, for example, weighs about one half of the comparable amount of aluminum but has considerably greater strength, particularly in the lateral direction (i.e. against the sides of the oval mast) and flexibility.
The aerodynamic qualities of a mast are determined, in part, by how accurately and uniformly the mast is manufactured A conventional fabric-resin mast, formed for example from fibreglass, is produced in two parts, as front and back halves, which are then joined together. Each half is created by applying the resin-impregnated fabric over an aluminum mandrel, which functions as a male mould. After joining the halves together the mast is tested for strength by deflection testing. If the mast does not have the required strength (i.e. resistance to deflection) in the lateral and fore-aft directions, as indicated by over-flexing at specific points, more fabric-resin must be wrapped around the exterior of the mast to augment the weak points. This tends to make the exterior surface of the mast uneven. To compensate, often a curable filling compound is applied and carefully sanded, to restore the uniformity in taper and aerodynamic shape of the exterior surface of the mast, and to create an aesthetically pleasing finished appearance. Only once the mast is completely finished to the required strength and aesthetic characteristics is the finishing paint and hardware applied.
This method of manufacturing the mast presents a number of disadvantages. The fabric-resin augmentation and patching/refinishing steps are extremely laborious. The application and sanding of the fabric-resin and filling compound must be performed manually, and frequently many hundreds of hours of manual labour are required to bring a mast to the strength and aesthetic appearance required by boat owners, which can take several months. The quality of the finish is dependent upon the skill of the finishing labourers. Moreover, the filling compound is denser than the fabric-resin, so the finishing process adds unnecessary weight to the mast without adding any structural strength or integrity. In fact, the filling compound is not as strong as the fabric-resin compound and does not adhere well to a cured fabric-resin such as fibreglass or carbon-graphite, so over time the filler compound will crack and separate from the mast. This is aesthetically unappealing, reduces the aerodynamic characteristics of the mast, and can reduce the longevity of the mast due to water seepage.
Once the mast has been finished and painted, a track for hoisting the mainsail must be affixed to the aft (trailing) side of the mast. In use the track will tend to be pulled away from the mast by the forces acting on the sail, so where the track is affixed by bolts typically the track is bolted to the mast every six inches or so, in an attempt to distribute the force of the track over the entire length of the mast. However, in a conventional mast the concentration of stress around the drill holes can result in cracking, which can allow the track to separate from the mast and occasionally allow water to seep into the mast. The track can be affixed to the mast by glue, in which case the track is held along its entire length, but the pulling force of the mainsail can still cause the track to separate from the mast, in this case peeling off the finishing paint with it, again rendering the mast susceptible to cracking and water seepage.